Aluminum paste pigment



Patented Apr. 1, 1952 2,591,245

UNITED STATES PATENT OFFICE 2,591,245 ALUMINUM PASTE PIGMENT .lunius D. Edwards, Oakmont, Pa., assignor to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application August 11, 1948, Serial No. 43,760

Claims. (01. 106-290) This invention relates in general, to improvepast pigment manufacture, which may be pracments in the production of metallic pigments ticed with beneficial results on paste pigments of suitable for use in the manufacture of paints, inks the order by weight, 68 to 85 per cent aluminum and coating compositions, and is more particularflake. 1y concerned with the processing of aluminum 5 The new and novel feature of the invention is paste pigments to impart improved reflectivity directed to a wet polishing procedure for leaf and stability to such products. )lOdLlClIlg paste pigments, or slurries, of the stat- It is a primary object of the invention to pro- (1 68 to 85 per cent. metal flake content, in the vide a method or methods of processing metallic presence of an addition of free leafing agent as pigments in paste form, as a step or series of steps a separate solid phase, as distinguished from in their manufacturing process, wherein-the addileafing agent present in solution. The mere prestion of a pigment leafing agent is a controlling ence of the added leafing agent as a solid phase, factor. or in solid form, is not sufficient in itself to im- The invention is primarily concerned with partthe improved benefits of the invention, The aluminum base pigments and is described in de wet polishing operation must also be performed tail in respect thereto. It should not be limited on the paste, adjusted to include the added solid in its application to aluminum, since other metals phase leafing agent, to bring about a distribution and their alloys will respond and be improved, of some of the added solid leafing agent on the when treated in accordance with the invention. surfaces of the already coated metallic flakes. A

There are numerous processes in commercial wet polishing operation that insures repeated use for producing metallic pigments of the derubbing of the solid leafing agent against the sired fineness to provide acceptable paint prodcoated metal flakes, is important to my invenucts. The process described in United States tion. A two-bladed industrial mixer, incorporat- Patent 2,002,891, issued May 23, 1935, to Everett ing a pair of sigmoidal-shaped blades, that pref- J. Hall, is one which has received wide acceptance erably rotate inwardly towards the central lonand is commercially termed a wet process in that gitud'inal axis of a cylindrical shell housing the c'omminution of the metallic pigment is carried blades, has also been found satisfactory for proout in a ball mill in a solution of leaf producing ducing the Wet polishing rubbing action that is agents, such as stearic acid and palmitic acid, and herein contemplated. It should be understood a volatilizable hydrocarb Such as mineral that other commercial forms of apparatus, such p t p o a t c p ment in the form as a burr mill, may be substituted for the indusof a sludge-like mass or paste characterized by trial mixer for carrying out the wet polishing opthe individual metallic flakes being coated with oration. v a fi o t leaf producing gent. The solid phase leafing agent may be added to he Sludge discharged from the ball mill is the paste pigments in the form of solid stearic filtered to remove a portion of the liquid phase acid or mixtures thereof with palmitic acid, or and provide an alum u pigment Cake 0f 4 other suitable leafing agents, or it may be added proxima c p s n y h b ut 80 p in the form of these leafing agents suspended Cent metal flake W th e l ce i l pirits or dispersed in mineral spirits, or other volatile n a n a m ll m nt f d ssolv d l fins hydrocarbons, and mixtures thereof. It is also t- In P e t practice, the cake is thereafter possible to dissolve solid leafing agent in a limitdjusted by the addition of a solution of clean ed amount of mineral spirits, as by heating a mixm ralSp s and ea n a e t 0 a aPD O ture of the same, and then permitting the mix mate Compos on by Weight, 60 t0 6 p r Cent ture to cool to permit the separation of solid leafalum um flake- T s ju d product s p ing agent to make it available for the subsequent ently sold as a widely known leafing aluminum wet polishing. Leafing agents in amounts be- Daste pigment for s qu t ad tu e W tween 1 and 4 per cent, expressed in terms of the suitable paint vehicles in the manufacture of t t l weight of aluminum paste pigments, have aluminum p The adjustment om filter been found satisfactory in the practice of the incake to themarketed product to per cent vention,

aluminum flake paste) is usually carried out in As previously stated in this specification, the a standard commercial mixer of the single blade, wet polishing treatment has been defined in terms cylindrical housing type. of a repeated rubbing action between the metal The present invention involves the introduction of a new and novel step, or steps, in aluminum flakes of a pigment paste formulation, in the presence of an added leafing agent in solid phase, to

polish the individual flakes and apply a further coating ofsolid phase leafing agent on the film bearing surfaces of the flakes.

It is not essential that a single step introduction of the solid phase leaflng agent be employed, nor is it necessary to carry out the wet polishing treatment without interruption. Periods of wet polishing, whether continuous or interrupted, ranging from about 1 to 12 hours total expired time, have been found satisfactory, with substan-' tial improvement being obtained within the lower time range of any selected wet polishing cycle, as measured in terms of improved stability and reflectivity in the pigments so treated, regardless of whether the solid phase leafing agent was added all at one time, or intermittently.

It is not essential that the leafing agent be.

present as a solid during an entire wet polishing cycle. For example, the wet polishing treatment is normally accompanied by a temperature rise which tends to dissolve some of the solid phase leafing agent in the liquid phase of the paste pi ment formulation, particularly as a wet polishing cycle progresses. In this connection, an upper temperature limit of 110 F. should not be exceeded. .It is essential to the benefits of the invention, however, that the solid phase leafing agent be present during a sufficient portion of a wet polishing cycle as to insure a substantial period of rubbing between the solid leafing agent and metallic flakes, as well as the distribution of an effective quantity of the added solid leafine' agent on the surfaces of the flakes.

In a commercial application of the method of the invention, leafing paste formulations of com-' pigments that had not been wet polished in accordance with the method of the invention.

Paste pigments, treated in accordance with the practices of the invention described above, may be adjusted to any desirable metallic flake and leaf ing agent content following the wet polishin treatment. Whetheror not the paste pigments are further adjusted in composition, the products are in condition, following wet polishing, for packaging and subsequent admixture with suitable paint vehicles, such as varnish. The paste pigments thus treated may also be converted to dry powder pigments by driving off the volatile hydrocarbons.

A conventional leafing paste pigment, produced without benefit of the wet polishing procedure of the invention, and having a nominal composition by-weight, 63 per cent aluminium flakes, 2 per cent stearic acid, and 35 grams of mineral spirits was mixed with a varnish vehicle to form a paint and applied to a steel panel. The dir- 'fusely reflected light measurement for this panel was 19 per cent, as obtained by a standard Hunter multipurpose reflectometer, which is described in the National Bureau of Standards Journal of Research, vol. 25, pages 581-618, November 1940.

-;A'paste pigment produced and treated in. ac-

, cordance with the wet polishing procedure of the invention, and having a nominal composition by weight, '72 per cent aluminum flakes, 2.25 per cent stearic acid, and 25.75 per cent mineral spirits, was mixed to the same formulation using the same varnish vehicle and the same pigment concentration as employed with the conventional paste pigment described above, and applied to a steel panel.- Using the Hunter multipurpose reflectometer, the difiusely reflected light was only 14 per cent and the panel exhibited a brighter and more metallic appearance.

. Stability tests on ready mixed paints were also conducted to compare the conventional paste pigments with pigments produced in accordance with the practice of the invention. An alkyd resin vehicle was selected for the vehicle portion of the ready mixed aluminum paints, since this particular type or vehicle was known to present a problem in leaf stability of ready mixed paints. A ready mixed paint made from conventional paste pigment-of 65 per cent aluminum flake content exhibited an initial leaf of 6d per cent, which dropped to zero leaf after three months storage. A ready mixed paint made to the same formula from paste pigment of '7 4 per cent aluminum flake content, which was produced in accordance with the practice of. the invention, exhibited an initial leaf of 68 per cent and only dropped to 5lper cent after three months storage. In both cases the ready mixed paints contained 14.5 per cent aluminum flake pigment, based on the total weight of ready mixed paint.

What is claimed is: r

1. In the production of aluminum paste pigment characterized by improved stability, brightness and specular reflectivity, the process'of subjecting a mixture comprising a main body of 68 to per cent aluminum flakes, coated with'a leaf-producing agent in the presence of about 14 to 28 per cent mineral spirits containing dissolved stearic acid, to a wet polishing operation effected by adding solid stearic acid in amounts between 1.0 to M) per cent of the total weight of the pigment and stirring the mixture so that flake rubs against flake for a period of about 1 to 12 hours, while maintaining the temperature below about F.

2. An aluminum paste pigment formulation comprising a main body of leafing aluminum flakes constituting from 68 to 85 per cent of the paste, about 1.0 to 4.0 per cent leafing agent, and

about 14 to 28 per cent mineralspirits, said flakes having been wet polished for a period of about 1 to 12 hours at a temperature not exceeding 110 F. in the presence of at least one of an added solid leafing agent of the group consisting of stearic and palmitic acids to efiect substantial improvement in brightness, specular reflectivity and leaf stability.

3. In the production of aluminum paste pigment characterized by improved stability, brightness and specular reflectivity, the process of subjecting a mixturecomprising a main body of 68 to 85 per cent aluminum flakes, coated with a leaf-producing agent and moistened with about 14 to 28 per cent by weight of mineral spirits, to a wet polishing operation for a period of about 1 to 12 hours in the presence of mixtures of stearic and palmitic acids added in solid phase in amounts between 1.0 to 4.0 per cent of the total weight of the pigment, while maintaining an operating temperature below about 110 F.

4. An aluminum paste pigment formulation comprising a main body of leafing aluminum flakes'constituting' from 68 to 85 per cent of the paste, about 14 to 28 per cent mineral spirits, and

at least one leaflng agent' of the group consisting of stearic and palmiticij eicids. said leafing agent having been added at least in part in solid phase in amounts between 1.0 to 4.0 per cent of the total weight of the pigment formulation and the paste; formulation wet polisl ed for a period of about? 1 to 12 hours at a temperature below about 110- FE, and said pigment formulation being characterized by improved (stability, brightness and specular reflectivity.

5. In the production of aluminum paste pigment characterized by' im'proved stability, brightness and specular refle vity, the process oi subjecting a mixture comprising a main body I to 85 per cent aluminum flakes, coated with'a leaf-producing agentat id moistened with'febout 14 to 28 per cent by weight of mineral spirits, to g wet polishing operetion for a period of fabout 1 to 12 hours in the presence of at least one leefing REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS} Number Name Date 2,144,953 Ziehl Jan n24, 1939 2,193,663

Arthur Mar. 12, 1940 OTHER REFERENCES 7 Aluminum Paint and Powder, Edwards, 2nd ed, Reinhold Pub. (30., New York, N, Y. 1935. 

4. AN ALUMINUM PASTE PIGMENT FORMULATION COMPRISING A MAIN BODY OF LEAFING ALUMINUM FLAKES CONSTITUTING FROM 68 TO 85 PER CENT OF THE PASTE, ABOUT 14 TO 28 PER CENT MINERAL SPIRITS, AND AT LEAST ONE LEAFING AGENT OF THE GROUP CONSISITING OF STEARIC AND PALMITIC ACIDS, SAID LEAFING AGENT HAVING BEEN ADDED AT LEAST IN PART IN SOLID PHASE IN AMOUNTS BETWEEN 1.0 TO 4.0 PER CENT OF THE TOTAL WEIGHT OF THE PIGMENT FORMULATION AND THE PASTE FORMULATION WET POLISHED FOR A PERIOD OF ABOUT 1 TO 12 HOURS AT A TEMPERATURE BELOW ABOUT 110* F., AND SAID PIGMENT FORMULATION BEING CHARACTERIZED BY IMPROVED STABILITY, BRIGHTNESS AND SPECULAR REFLECTIVITY. 